Commonly used thermal neutron detectors such as gas proportional counters and scintillation counters tend to be bulky and are not readily configured for covering large areas. Gas proportional counters require high voltages, on the order of kilovolts, which can be electronically noisy and susceptible to arcing due to environmental conditions. Solid-state neutron detectors based on silicon or germanium photodiodes and phototransistors exist, but they tend to have small detection apertures, and typically require a neutron converter foil, such as Gd, in front of the semiconductor device. One class of solid-state neutron-detectors detects electron-hole pairs that cross a semiconductor junction. The electron hole pairs are produced by reaction particles formed as a result of neutron reaction within films containing neutron-sensitive material incorporated within the detector. One such solid-state neutron detector includes a silicon semiconductor having a layer doped with boron. Neutrons react with the boron-containing layer, thereby creating energetic reaction particles that, in turn, create electron-hole pairs that diffuse into and across the junction to produce a current pulse.
Boron-rich solid-state neutron detectors have been described by B. W. Robertson, et al., in Applied Physics Letters, Volume 80, No. 19, pp. 3644-3646 (May 2002). However, a significant problem with these solid-state neutron detectors is the difficulty of forming ohmic contacts to the boron compound layer, which is a semiconducting material. Examples of a boron compound include boron carbide (B5C). For the above-referenced detector, intervening semiconducting layers are used between the boron carbide layer and the electrodes. However, forming multiple layers is expensive because each layer requires individual processing to create a structure that has good electrical conductance and adhesion between the multiple layers and the boron carbide layer. Also, the interface between the two semiconducting layers creates a diode structure, and thus a rectifying contact to the boron-containing layer. Such a diode structure is operated with a reverse bias voltage applied, which can lead to an unacceptably high background, or dark, current. Therefore, a need exists for a solid-state neutron detector for which low-resistance (or ohmic) contacts or electrodes may be formed directly onto the semiconducting boron-containing layer, and that operates with a low background current.